Attempts have been made in recent years to apply woodgrain patterns and/or woody texture of natural wood to molded products made of chlorine-containing resins such as vinyl chloride, and to use those molded products, which have been provided with color tones and texture close to those of natural wood, as e.g. interior materials for cars, side moldings, interior materials for houses, building materials such as exterior cladding, floor materials for terraces, balconies, decks, etc., materials for civil works, wooden causeways provided e.g. in wetlands in natural parks, handrails made by covering steel pipes, frames for tables, and gaskets (see Patent Documents 1 and 2).
The chlorine-containing resins used for the above products contain a large amount of chlorine in their molecules, and thus have excellent flame-retardant properties. However, the addition of wood flour, which is a flammable material, may impair the resin's flame-retardant properties. Further, chlorine-containing resins are disadvantageous in that they produce chlorine gas or hydrogen chloride gas when exposed to high temperatures above its heatproof temperature in case of fire etc. because they contain chlorine in their molecules, and they also produce toxic gases, such as carbon monoxide, as well as heavy smoke at the time of combustion.
To improve flame-retardant properties of chlorine-containing resins, attempts have been made heretofore to blend antimony trioxide into the resins. The use of antimony trioxide indeed improves flame-retardant properties, but instead tends to worsen the properties relating to emission of smoke and provides no countermeasure against the production of toxic gases, in particular, hydrogen chloride gas and carbon monoxide gas. Antimony trioxide also suffers from containing toxic components such as lead and arsenic as impurities originating from its ore.
Phosphoric ester-based flame retardants have also been used heretofore. For example, Patent Document 3 proposes the combined use of a phosphoric ester flame retardant and zinc hydroxystannate. This countermeasure, however, is also insufficient in restraining smoke emission, and cannot sufficiently restrain the production of toxic gases such as carbon monoxide.
Patent Document 4 proposes a soft vinyl chloride resin composition that achieves low smoke emission by combinedly using a zinc compound, antimony trioxide, and a phosphoric ester. Patent Document 5 proposes a vinyl chloride resin composition for electric wires that achieves low smoke emission by combinedly using an inorganic compound and a condensation organophosphorus compound. However, the low smoke emission properties of these vinyl chloride resin compositions are still insufficient. Further, these countermeasures give no consideration to the emission of toxic carbon monoxide gas and thus cannot prevent emission thereof, nor do these Patent Document provide information about restraining production of carbon monoxide.
Further, Patent Documents 6 and 7 propose synthetic resin compositions that contain flame retardants obtained by combining specific types of phosphates, professing that no harmful gas is emitted at the time of combustion. However, the expression “no harmful gas is emitted” as used in these Patent Documents merely means that there is no emission of harmful gas originating from halogen-based flame retardants (i.e., chlorine gas, hydrogen chloride gas, etc.) because no halogen-based flame retardant is used. This is completely different from the concept of the present invention. Further, Patent Documents 6 and 7 give chlorine-containing resins, such as polyvinyl chloride, as examples of synthetic resins, but they merely provide a list of generally-used synthetic resins and provide no concrete working example. Furthermore, these Patent Documents provide no disclosure nor information about restraining emission of smoke and production of toxic gases, such as carbon monoxide, other than harmful gases originating from halogen.    Patent Document 1: JP-A-10-231405    Patent Document 2: JP-A-9-239707    Patent Document 3: JP-A-5-331336    Patent Document 4: JP-A-5-51504    Patent Document 5: JP-A-7-149982    Patent Document 6: JP-A-2003-26935    Patent Document 7: JP-A-2004-238568